Symphytum officinale: Russian comfrey

Family

Boraginaceae

Common Names

Common comfrey (S. officinale), Russian comfrey (S. x uplandicum, a hybrid of A. asperum x A. officinale), rough comfrey (S. asperum), and tuberous comfrey (S. tuberosum) are the most common species encountered in North America.

Plant Description

Comprising some 25 species, Symphytum species are native to Europe and the Mediterranean area with several species now commonly grown or escaped in North America. Rapidly growing and invasive perennials growing from taproots or rhizomes, erect, branching, up to 200cm in height and generally covered with stiff hairs. Stems may have wings.

Leaves are alternate with the uppermost leaves being crowded opposite, petiolate, and lanceolate. Flowers are produced terminally or axillary, on short, branching cymes, each terminating in 5 triangular lobes. Colors vary from blue, pink, cream, to white (Fig. 379 and Fig. 380).

Fruits are 4 ridged nutlets.

Figure 379. Symphytum officinale.

Figure 380. Symphytum officinale flowers.

Toxic Principle and Mechanism of Action

A variety of hepatotoxic pyrrolizidine alkaloids (PA) have been identified in the leaves and roots of Russian comfrey (Symphytum x uplandicum) and common comfrey (S. officinale) [1-3]. Especially in combination, the PA cause chronic hepatotoxicity in animals and humans [1,4,5]. The alkaloids are also carcinogenic and therefore are hazardous to people or animals that are fed medicinal supplements containing comfrey [6,7].

The PA are converted by the liver into toxic pyrroles that inhibit cellular protein synthesis and cell mitosis [8,9]. Hepatocyte necrosis, degeneration and liver fibrosis with biliary hyperplasia characterize the toxic effects of the pyrrolizidine alkaloids. The alkaloids are passed through the milk of lactating animals and therefore pose a potential risk to suckling animals [10].

Risk Assessment

There is relatively little risk of comfrey causing poisoning in animals unless they are fed over a period of time supplements containing comfrey. Since the plants can become invasive, care should be taken to see that comfrey does not get into hay meadows, or is fed as garden clippings to corralled livestock.

Clinical Signs

Animals that consume PA containing plants over a period of time develop signs of liver failure. Horses and cattle are generally the most severely affected, while sheep and goats are quite resistant to PA toxicity. Weight loss, icterus, diarrhea, photosensitization, and neurologic signs related to hepatic encephalopathy are typical of liver failure. Serum liver enzymes are generally elevated significantly. Similarly, people who chronically consume comfrey teas and other herbal preparations containing comfrey may develop serious liver veno-occlusive disease.

Confirmation of PA toxicity can be made by a liver a biopsy that shows the triad of histological changes characteristic of PA poisoning, namely liver megalocytosis, fibrosis, and biliary hyperplasia [11].

Treatment of animals with PA poisoning is generally limited to placing the animal in a barn out of the sun to relieve the photosensitization, providing a high quality, low protein diet, and removing all sources of the PA from the animal’s food. The prognosis is generally very poor since once clinical signs of liver failure from PA poisoning occur, the degree of liver damage is severe and irreversible.